diff options
Diffstat (limited to 'library/std/src/thread')
| -rw-r--r-- | library/std/src/thread/local.rs | 567 | ||||
| -rw-r--r-- | library/std/src/thread/mod.rs | 40 |
2 files changed, 3 insertions, 604 deletions
diff --git a/library/std/src/thread/local.rs b/library/std/src/thread/local.rs index cf7c2e05a..7fdf03acc 100644 --- a/library/std/src/thread/local.rs +++ b/library/std/src/thread/local.rs @@ -173,200 +173,6 @@ macro_rules! thread_local { ); } -#[doc(hidden)] -#[unstable(feature = "thread_local_internals", reason = "should not be necessary", issue = "none")] -#[macro_export] -#[allow_internal_unstable(thread_local_internals, cfg_target_thread_local, thread_local)] -#[allow_internal_unsafe] -macro_rules! __thread_local_inner { - // used to generate the `LocalKey` value for const-initialized thread locals - (@key $t:ty, const $init:expr) => {{ - #[cfg_attr(not(windows), inline)] // see comments below - #[deny(unsafe_op_in_unsafe_fn)] - unsafe fn __getit( - _init: $crate::option::Option<&mut $crate::option::Option<$t>>, - ) -> $crate::option::Option<&'static $t> { - const INIT_EXPR: $t = $init; - - // wasm without atomics maps directly to `static mut`, and dtors - // aren't implemented because thread dtors aren't really a thing - // on wasm right now - // - // FIXME(#84224) this should come after the `target_thread_local` - // block. - #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] - { - static mut VAL: $t = INIT_EXPR; - unsafe { $crate::option::Option::Some(&VAL) } - } - - // If the platform has support for `#[thread_local]`, use it. - #[cfg(all( - target_thread_local, - not(all(target_family = "wasm", not(target_feature = "atomics"))), - ))] - { - #[thread_local] - static mut VAL: $t = INIT_EXPR; - - // If a dtor isn't needed we can do something "very raw" and - // just get going. - if !$crate::mem::needs_drop::<$t>() { - unsafe { - return $crate::option::Option::Some(&VAL) - } - } - - // 0 == dtor not registered - // 1 == dtor registered, dtor not run - // 2 == dtor registered and is running or has run - #[thread_local] - static mut STATE: $crate::primitive::u8 = 0; - - unsafe extern "C" fn destroy(ptr: *mut $crate::primitive::u8) { - let ptr = ptr as *mut $t; - - unsafe { - $crate::debug_assert_eq!(STATE, 1); - STATE = 2; - $crate::ptr::drop_in_place(ptr); - } - } - - unsafe { - match STATE { - // 0 == we haven't registered a destructor, so do - // so now. - 0 => { - $crate::thread::__FastLocalKeyInner::<$t>::register_dtor( - $crate::ptr::addr_of_mut!(VAL) as *mut $crate::primitive::u8, - destroy, - ); - STATE = 1; - $crate::option::Option::Some(&VAL) - } - // 1 == the destructor is registered and the value - // is valid, so return the pointer. - 1 => $crate::option::Option::Some(&VAL), - // otherwise the destructor has already run, so we - // can't give access. - _ => $crate::option::Option::None, - } - } - } - - // On platforms without `#[thread_local]` we fall back to the - // same implementation as below for os thread locals. - #[cfg(all( - not(target_thread_local), - not(all(target_family = "wasm", not(target_feature = "atomics"))), - ))] - { - #[inline] - const fn __init() -> $t { INIT_EXPR } - static __KEY: $crate::thread::__OsLocalKeyInner<$t> = - $crate::thread::__OsLocalKeyInner::new(); - #[allow(unused_unsafe)] - unsafe { - __KEY.get(move || { - if let $crate::option::Option::Some(init) = _init { - if let $crate::option::Option::Some(value) = init.take() { - return value; - } else if $crate::cfg!(debug_assertions) { - $crate::unreachable!("missing initial value"); - } - } - __init() - }) - } - } - } - - unsafe { - $crate::thread::LocalKey::new(__getit) - } - }}; - - // used to generate the `LocalKey` value for `thread_local!` - (@key $t:ty, $init:expr) => { - { - #[inline] - fn __init() -> $t { $init } - - // When reading this function you might ask "why is this inlined - // everywhere other than Windows?", and that's a very reasonable - // question to ask. The short story is that it segfaults rustc if - // this function is inlined. The longer story is that Windows looks - // to not support `extern` references to thread locals across DLL - // boundaries. This appears to at least not be supported in the ABI - // that LLVM implements. - // - // Because of this we never inline on Windows, but we do inline on - // other platforms (where external references to thread locals - // across DLLs are supported). A better fix for this would be to - // inline this function on Windows, but only for "statically linked" - // components. For example if two separately compiled rlibs end up - // getting linked into a DLL then it's fine to inline this function - // across that boundary. It's only not fine to inline this function - // across a DLL boundary. Unfortunately rustc doesn't currently - // have this sort of logic available in an attribute, and it's not - // clear that rustc is even equipped to answer this (it's more of a - // Cargo question kinda). This means that, unfortunately, Windows - // gets the pessimistic path for now where it's never inlined. - // - // The issue of "should enable on Windows sometimes" is #84933 - #[cfg_attr(not(windows), inline)] - unsafe fn __getit( - init: $crate::option::Option<&mut $crate::option::Option<$t>>, - ) -> $crate::option::Option<&'static $t> { - #[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] - static __KEY: $crate::thread::__StaticLocalKeyInner<$t> = - $crate::thread::__StaticLocalKeyInner::new(); - - #[thread_local] - #[cfg(all( - target_thread_local, - not(all(target_family = "wasm", not(target_feature = "atomics"))), - ))] - static __KEY: $crate::thread::__FastLocalKeyInner<$t> = - $crate::thread::__FastLocalKeyInner::new(); - - #[cfg(all( - not(target_thread_local), - not(all(target_family = "wasm", not(target_feature = "atomics"))), - ))] - static __KEY: $crate::thread::__OsLocalKeyInner<$t> = - $crate::thread::__OsLocalKeyInner::new(); - - // FIXME: remove the #[allow(...)] marker when macros don't - // raise warning for missing/extraneous unsafe blocks anymore. - // See https://github.com/rust-lang/rust/issues/74838. - #[allow(unused_unsafe)] - unsafe { - __KEY.get(move || { - if let $crate::option::Option::Some(init) = init { - if let $crate::option::Option::Some(value) = init.take() { - return value; - } else if $crate::cfg!(debug_assertions) { - $crate::unreachable!("missing default value"); - } - } - __init() - }) - } - } - - unsafe { - $crate::thread::LocalKey::new(__getit) - } - } - }; - ($(#[$attr:meta])* $vis:vis $name:ident, $t:ty, $($init:tt)*) => { - $(#[$attr])* $vis const $name: $crate::thread::LocalKey<$t> = - $crate::__thread_local_inner!(@key $t, $($init)*); - } -} - /// An error returned by [`LocalKey::try_with`](struct.LocalKey.html#method.try_with). #[stable(feature = "thread_local_try_with", since = "1.26.0")] #[non_exhaustive] @@ -779,376 +585,3 @@ impl<T: 'static> LocalKey<RefCell<T>> { self.with(|cell| cell.replace(value)) } } - -mod lazy { - use crate::cell::UnsafeCell; - use crate::hint; - use crate::mem; - - pub struct LazyKeyInner<T> { - inner: UnsafeCell<Option<T>>, - } - - impl<T> LazyKeyInner<T> { - pub const fn new() -> LazyKeyInner<T> { - LazyKeyInner { inner: UnsafeCell::new(None) } - } - - pub unsafe fn get(&self) -> Option<&'static T> { - // SAFETY: The caller must ensure no reference is ever handed out to - // the inner cell nor mutable reference to the Option<T> inside said - // cell. This make it safe to hand a reference, though the lifetime - // of 'static is itself unsafe, making the get method unsafe. - unsafe { (*self.inner.get()).as_ref() } - } - - /// The caller must ensure that no reference is active: this method - /// needs unique access. - pub unsafe fn initialize<F: FnOnce() -> T>(&self, init: F) -> &'static T { - // Execute the initialization up front, *then* move it into our slot, - // just in case initialization fails. - let value = init(); - let ptr = self.inner.get(); - - // SAFETY: - // - // note that this can in theory just be `*ptr = Some(value)`, but due to - // the compiler will currently codegen that pattern with something like: - // - // ptr::drop_in_place(ptr) - // ptr::write(ptr, Some(value)) - // - // Due to this pattern it's possible for the destructor of the value in - // `ptr` (e.g., if this is being recursively initialized) to re-access - // TLS, in which case there will be a `&` and `&mut` pointer to the same - // value (an aliasing violation). To avoid setting the "I'm running a - // destructor" flag we just use `mem::replace` which should sequence the - // operations a little differently and make this safe to call. - // - // The precondition also ensures that we are the only one accessing - // `self` at the moment so replacing is fine. - unsafe { - let _ = mem::replace(&mut *ptr, Some(value)); - } - - // SAFETY: With the call to `mem::replace` it is guaranteed there is - // a `Some` behind `ptr`, not a `None` so `unreachable_unchecked` - // will never be reached. - unsafe { - // After storing `Some` we want to get a reference to the contents of - // what we just stored. While we could use `unwrap` here and it should - // always work it empirically doesn't seem to always get optimized away, - // which means that using something like `try_with` can pull in - // panicking code and cause a large size bloat. - match *ptr { - Some(ref x) => x, - None => hint::unreachable_unchecked(), - } - } - } - - /// The other methods hand out references while taking &self. - /// As such, callers of this method must ensure no `&` and `&mut` are - /// available and used at the same time. - #[allow(unused)] - pub unsafe fn take(&mut self) -> Option<T> { - // SAFETY: See doc comment for this method. - unsafe { (*self.inner.get()).take() } - } - } -} - -/// On some targets like wasm there's no threads, so no need to generate -/// thread locals and we can instead just use plain statics! -#[doc(hidden)] -#[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] -pub mod statik { - use super::lazy::LazyKeyInner; - use crate::fmt; - - pub struct Key<T> { - inner: LazyKeyInner<T>, - } - - unsafe impl<T> Sync for Key<T> {} - - impl<T> fmt::Debug for Key<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("Key").finish_non_exhaustive() - } - } - - impl<T> Key<T> { - pub const fn new() -> Key<T> { - Key { inner: LazyKeyInner::new() } - } - - pub unsafe fn get(&self, init: impl FnOnce() -> T) -> Option<&'static T> { - // SAFETY: The caller must ensure no reference is ever handed out to - // the inner cell nor mutable reference to the Option<T> inside said - // cell. This make it safe to hand a reference, though the lifetime - // of 'static is itself unsafe, making the get method unsafe. - let value = unsafe { - match self.inner.get() { - Some(ref value) => value, - None => self.inner.initialize(init), - } - }; - - Some(value) - } - } -} - -#[doc(hidden)] -#[cfg(all(target_thread_local, not(all(target_family = "wasm", not(target_feature = "atomics"))),))] -pub mod fast { - use super::lazy::LazyKeyInner; - use crate::cell::Cell; - use crate::sys::thread_local_dtor::register_dtor; - use crate::{fmt, mem, panic}; - - #[derive(Copy, Clone)] - enum DtorState { - Unregistered, - Registered, - RunningOrHasRun, - } - - // This data structure has been carefully constructed so that the fast path - // only contains one branch on x86. That optimization is necessary to avoid - // duplicated tls lookups on OSX. - // - // LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722 - pub struct Key<T> { - // If `LazyKeyInner::get` returns `None`, that indicates either: - // * The value has never been initialized - // * The value is being recursively initialized - // * The value has already been destroyed or is being destroyed - // To determine which kind of `None`, check `dtor_state`. - // - // This is very optimizer friendly for the fast path - initialized but - // not yet dropped. - inner: LazyKeyInner<T>, - - // Metadata to keep track of the state of the destructor. Remember that - // this variable is thread-local, not global. - dtor_state: Cell<DtorState>, - } - - impl<T> fmt::Debug for Key<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("Key").finish_non_exhaustive() - } - } - - impl<T> Key<T> { - pub const fn new() -> Key<T> { - Key { inner: LazyKeyInner::new(), dtor_state: Cell::new(DtorState::Unregistered) } - } - - // note that this is just a publicly-callable function only for the - // const-initialized form of thread locals, basically a way to call the - // free `register_dtor` function defined elsewhere in std. - pub unsafe fn register_dtor(a: *mut u8, dtor: unsafe extern "C" fn(*mut u8)) { - unsafe { - register_dtor(a, dtor); - } - } - - pub unsafe fn get<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> { - // SAFETY: See the definitions of `LazyKeyInner::get` and - // `try_initialize` for more information. - // - // The caller must ensure no mutable references are ever active to - // the inner cell or the inner T when this is called. - // The `try_initialize` is dependant on the passed `init` function - // for this. - unsafe { - match self.inner.get() { - Some(val) => Some(val), - None => self.try_initialize(init), - } - } - } - - // `try_initialize` is only called once per fast thread local variable, - // except in corner cases where thread_local dtors reference other - // thread_local's, or it is being recursively initialized. - // - // Macos: Inlining this function can cause two `tlv_get_addr` calls to - // be performed for every call to `Key::get`. - // LLVM issue: https://bugs.llvm.org/show_bug.cgi?id=41722 - #[inline(never)] - unsafe fn try_initialize<F: FnOnce() -> T>(&self, init: F) -> Option<&'static T> { - // SAFETY: See comment above (this function doc). - if !mem::needs_drop::<T>() || unsafe { self.try_register_dtor() } { - // SAFETY: See comment above (this function doc). - Some(unsafe { self.inner.initialize(init) }) - } else { - None - } - } - - // `try_register_dtor` is only called once per fast thread local - // variable, except in corner cases where thread_local dtors reference - // other thread_local's, or it is being recursively initialized. - unsafe fn try_register_dtor(&self) -> bool { - match self.dtor_state.get() { - DtorState::Unregistered => { - // SAFETY: dtor registration happens before initialization. - // Passing `self` as a pointer while using `destroy_value<T>` - // is safe because the function will build a pointer to a - // Key<T>, which is the type of self and so find the correct - // size. - unsafe { register_dtor(self as *const _ as *mut u8, destroy_value::<T>) }; - self.dtor_state.set(DtorState::Registered); - true - } - DtorState::Registered => { - // recursively initialized - true - } - DtorState::RunningOrHasRun => false, - } - } - } - - unsafe extern "C" fn destroy_value<T>(ptr: *mut u8) { - let ptr = ptr as *mut Key<T>; - - // SAFETY: - // - // The pointer `ptr` has been built just above and comes from - // `try_register_dtor` where it is originally a Key<T> coming from `self`, - // making it non-NUL and of the correct type. - // - // Right before we run the user destructor be sure to set the - // `Option<T>` to `None`, and `dtor_state` to `RunningOrHasRun`. This - // causes future calls to `get` to run `try_initialize_drop` again, - // which will now fail, and return `None`. - // - // Wrap the call in a catch to ensure unwinding is caught in the event - // a panic takes place in a destructor. - if let Err(_) = panic::catch_unwind(panic::AssertUnwindSafe(|| unsafe { - let value = (*ptr).inner.take(); - (*ptr).dtor_state.set(DtorState::RunningOrHasRun); - drop(value); - })) { - rtabort!("thread local panicked on drop"); - } - } -} - -#[doc(hidden)] -#[cfg(all( - not(target_thread_local), - not(all(target_family = "wasm", not(target_feature = "atomics"))), -))] -pub mod os { - use super::lazy::LazyKeyInner; - use crate::cell::Cell; - use crate::sys_common::thread_local_key::StaticKey as OsStaticKey; - use crate::{fmt, marker, panic, ptr}; - - /// Use a regular global static to store this key; the state provided will then be - /// thread-local. - pub struct Key<T> { - // OS-TLS key that we'll use to key off. - os: OsStaticKey, - marker: marker::PhantomData<Cell<T>>, - } - - impl<T> fmt::Debug for Key<T> { - fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { - f.debug_struct("Key").finish_non_exhaustive() - } - } - - unsafe impl<T> Sync for Key<T> {} - - struct Value<T: 'static> { - inner: LazyKeyInner<T>, - key: &'static Key<T>, - } - - impl<T: 'static> Key<T> { - #[rustc_const_unstable(feature = "thread_local_internals", issue = "none")] - pub const fn new() -> Key<T> { - Key { os: OsStaticKey::new(Some(destroy_value::<T>)), marker: marker::PhantomData } - } - - /// It is a requirement for the caller to ensure that no mutable - /// reference is active when this method is called. - pub unsafe fn get(&'static self, init: impl FnOnce() -> T) -> Option<&'static T> { - // SAFETY: See the documentation for this method. - let ptr = unsafe { self.os.get() as *mut Value<T> }; - if ptr.addr() > 1 { - // SAFETY: the check ensured the pointer is safe (its destructor - // is not running) + it is coming from a trusted source (self). - if let Some(ref value) = unsafe { (*ptr).inner.get() } { - return Some(value); - } - } - // SAFETY: At this point we are sure we have no value and so - // initializing (or trying to) is safe. - unsafe { self.try_initialize(init) } - } - - // `try_initialize` is only called once per os thread local variable, - // except in corner cases where thread_local dtors reference other - // thread_local's, or it is being recursively initialized. - unsafe fn try_initialize(&'static self, init: impl FnOnce() -> T) -> Option<&'static T> { - // SAFETY: No mutable references are ever handed out meaning getting - // the value is ok. - let ptr = unsafe { self.os.get() as *mut Value<T> }; - if ptr.addr() == 1 { - // destructor is running - return None; - } - - let ptr = if ptr.is_null() { - // If the lookup returned null, we haven't initialized our own - // local copy, so do that now. - let ptr = Box::into_raw(Box::new(Value { inner: LazyKeyInner::new(), key: self })); - // SAFETY: At this point we are sure there is no value inside - // ptr so setting it will not affect anyone else. - unsafe { - self.os.set(ptr as *mut u8); - } - ptr - } else { - // recursive initialization - ptr - }; - - // SAFETY: ptr has been ensured as non-NUL just above an so can be - // dereferenced safely. - unsafe { Some((*ptr).inner.initialize(init)) } - } - } - - unsafe extern "C" fn destroy_value<T: 'static>(ptr: *mut u8) { - // SAFETY: - // - // The OS TLS ensures that this key contains a null value when this - // destructor starts to run. We set it back to a sentinel value of 1 to - // ensure that any future calls to `get` for this thread will return - // `None`. - // - // Note that to prevent an infinite loop we reset it back to null right - // before we return from the destructor ourselves. - // - // Wrap the call in a catch to ensure unwinding is caught in the event - // a panic takes place in a destructor. - if let Err(_) = panic::catch_unwind(|| unsafe { - let ptr = Box::from_raw(ptr as *mut Value<T>); - let key = ptr.key; - key.os.set(ptr::invalid_mut(1)); - drop(ptr); - key.os.set(ptr::null_mut()); - }) { - rtabort!("thread local panicked on drop"); - } - } -} diff --git a/library/std/src/thread/mod.rs b/library/std/src/thread/mod.rs index 489af7767..13b845b25 100644 --- a/library/std/src/thread/mod.rs +++ b/library/std/src/thread/mod.rs @@ -131,7 +131,8 @@ //! //! * Build the thread with [`Builder`] and pass the desired stack size to [`Builder::stack_size`]. //! * Set the `RUST_MIN_STACK` environment variable to an integer representing the desired stack -//! size (in bytes). Note that setting [`Builder::stack_size`] will override this. +//! size (in bytes). Note that setting [`Builder::stack_size`] will override this. Be aware that +//! changes to `RUST_MIN_STACK` may be ignored after program start. //! //! Note that the stack size of the main thread is *not* determined by Rust. //! @@ -203,44 +204,9 @@ pub use self::local::{AccessError, LocalKey}; // by the elf linker. "static" is for single-threaded platforms where a global // static is sufficient. -#[unstable(feature = "libstd_thread_internals", issue = "none")] -#[cfg(not(test))] -#[cfg(all( - target_thread_local, - not(all(target_family = "wasm", not(target_feature = "atomics"))), -))] -#[doc(hidden)] -pub use self::local::fast::Key as __FastLocalKeyInner; -// when building for tests, use real std's type -#[unstable(feature = "libstd_thread_internals", issue = "none")] -#[cfg(test)] -#[cfg(all( - target_thread_local, - not(all(target_family = "wasm", not(target_feature = "atomics"))), -))] -pub use realstd::thread::__FastLocalKeyInner; - -#[unstable(feature = "libstd_thread_internals", issue = "none")] -#[cfg(not(test))] -#[cfg(all( - not(target_thread_local), - not(all(target_family = "wasm", not(target_feature = "atomics"))), -))] #[doc(hidden)] -pub use self::local::os::Key as __OsLocalKeyInner; -// when building for tests, use real std's type -#[unstable(feature = "libstd_thread_internals", issue = "none")] -#[cfg(test)] -#[cfg(all( - not(target_thread_local), - not(all(target_family = "wasm", not(target_feature = "atomics"))), -))] -pub use realstd::thread::__OsLocalKeyInner; - #[unstable(feature = "libstd_thread_internals", issue = "none")] -#[cfg(all(target_family = "wasm", not(target_feature = "atomics")))] -#[doc(hidden)] -pub use self::local::statik::Key as __StaticLocalKeyInner; +pub use crate::sys::common::thread_local::Key as __LocalKeyInner; //////////////////////////////////////////////////////////////////////////////// // Builder |